It is known to provide electromechanical switches, for example in the form of relays and circuit breakers within electricity distribution systems. The purpose of relays is to control the flow of energy from one place to another, whereas the primary purpose of a circuit breaker is more protective, in that it seeks to prevent damage from occurring in over voltage or over current conditions by becoming open circuit.
In order to reliably detect the status of a relay or a circuit breaker, such relays or circuit breakers often have additional sensing contacts formed on the armature which moves to open or close the primary current flow path associated with the armature. Thus the sensing contacts enable a sensing signal to be applied to the relay to confirm whether the relay is open or closed. This stops unexpected fault modes, which may result from failure of a relay coil or sensing circuitry associated with a relay or circuit breaker from remaining hidden to the power distribution system or to a control system associated with the power distribution system.
Manufacturers and installers of relay and circuit breaker monitoring equipment have applied monitoring signals to the sensing contacts. However, the magnitude of the signals chosen has not benefitted from the provision of international standards and varies by manufacturer, application and country. Thus some manufacturers and installers have chosen to use relatively low sensing voltages, for example in the 5 to 10 volt range, whereas other manufacturers and installers have used sensing voltages at the prevailing mains distribution voltage, and therefore such voltages may be in the 115 volt range, 230-240 volt range or even higher. This inhibits the provision of equipment which is interoperable with the various relay control and monitoring systems installed around the world.